Orthodontic bracket

ABSTRACT

An orthodontic bracket is provided including a plastic bracket body and a metal reinforcement member partly embedded in the bracket body. The bracket body includes a slot extending substantially along a mesial-distal axis of the bracket body for receiving an arch wire. The reinforcement member includes a holding notch having a width that is smaller than that of the slot of the bracket body. The holding notch is positioned inside the slot and spaced-apart from the slot surfaces to form an arch wire holding mechanism for engaging the arch wire and to substantially avoid contact between the arch wire and the surfaces of the slot. The bracket body may further include removable markings on the lingual and/or labial surfaces to facilitate positioning of the bracket.

This application is a division of application Ser. No. 08/293,997, filedon Aug. 22, 1994, now U.S. Pat. No. 5,595,484.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to orthodontic brackets and,particularly, to plastic orthodontic brackets having a metalreinforcement member therein.

BACKGROUND OF THE INVENTION

Transparent or semi-transparent ceramic orthodontic brackets are moreaesthetically appealing than conventional metal brackets. However, oneproblem with ceramic brackets is that they are generally harder thantooth enamel, which may create tooth wear problems during occlusion.

Transparent or semi-transparent plastic brackets have problems ofcracking or deforming when torque is applied to the bracket byrectangular arch wires. Plastic brackets are also generally easilydiscolored by substances like coffee. However, resins with lowabsorption coefficients have been developed for use in plastic bracketsthat inhibit discoloring by substances like coffee.

Plastic brackets having a reinforcement member therein have also beendeveloped as disclosed in U.S. Pat. Nos. 3,930,311; 4,299,569; and4,302,532. The durability of a plastic bracket can be increased byinserting a metal reinforcement member therein to inhibit cracking ordeformation of the bracket.

Known metal reinforcement members for reinforced plastic bracketsdisclosed in U.S. Pat. No. 3,930,311 are stamped from sheet metal andinclude a holding notch therein having the same width as the slot of theplastic bracket body. The reinforcement member is inserted in thebracket body such that the holding notch is flush with the surfaces ofthe slot in the bracket body. An arch wire placed in the slot will thusbe in contact with the plastic surfaces of the slot as in unreinforcedplastic brackets. Such contact between the arch wire and the plasticsurfaces may make movement of the bracket relative to the arch wiredifficult and lengthen the time of orthodontic treatment.

Another problem in U.S. Pat. Nos. 4,299,569 and 4,302,532 is easyremoval of metal reinforcement during clinical application.

The coefficient of static friction between arch wires made fromstainless steel or a nickel-titanium alloy and metal surfaces is about0.15 to 0.2. By contrast, the coefficient of friction between the archwire and plastic surfaces is about 0.4 to 0.6. Accordingly, smoothmovement of the bracket with respect to an arch wire is difficult toachieve in known reinforced plastic brackets.

Furthermore, if known reinforced plastic brackets are to be providedwith torque-angulation, a large variety of metal reinforcement memberswill be needed to provide brackets adapted for use with various types ofteeth, orthodontist techniques and individual patient cases as shown inFIGS. 11 and 12 of U.S. Pat. No. 3,930,311. The costs for making such avariety of reinforcement members are high because many metal molds andstamping plates are required.

Moreover, in known reinforced plastic brackets, the inserted metalreinforcement member is designed to be substantially large to reinforcethe slot and wing portions of the bracket. The reinforcement membershown in FIGS. 16 and 17 of U.S. Pat. No. 3,930,311 includes a wide basewith a plurality of holes. The large size of the reinforcement membermay however make the plastic bracket less aesthetically appealing.

SUMMARY OF THE INVENTION

The present invention is directed at overcoming various problems ofknown reinforced plastic brackets. In accordance with the invention, areinforcement member having a holding notch is embedded in a plasticbracket body. The width of the holding notch is less than the width ofthe slot formed in the bracket body. The holding notch is located in theslot such that an arch wire can be engaged by the holding notch tosubstantially avoid contact with the surfaces of the slot.

The reinforcement member is designed to be used in brackets with orwithout torque-angulation. If the reinforcement member is made of ametallic material, it is preferably coated or plated to give it a whiterappearance.

In accordance with another embodiment of the invention, the base of abracket including a filler material therein may be irradiated to createa base surface that can be more securely bonded to a tooth. Inaccordance with a further embodiment of the invention, an inorganicphase may be formed on the base surface of a bracket, and a silanecoupling agent may be applied on the inorganic phase for more securelybonding the bracket to a tooth.

Brackets in accordance with the present invention differ from knownreinforced brackets in that the holding notch of the reinforcementmember forms the effective arch wire slot of the bracket. The holdingnotch of the reinforcement member has a smaller width than the slot ofthe bracket body such that the notch projects inside the slot.Accordingly, an arch wire can be engaged by the projected holding notchsuch that contact between the arch wire and the plastic slot surface ofthe bracket body is substantially avoided. The durability of the bracketis thus increased, while allowing a bracket affixed to a tooth to besmoothly moved along the arch wire.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a bracket in accordance with a firstembodiment of the invention illustrating the bracket body and thereinforcement member.

FIG. 2 is side view of the FIG. 1 bracket.

FIG. 3 is a front view of the FIG. 1 bracket.

FIGS. 4(A) and 4(B) are cross-section views of a mold apparatusillustrating different steps in the fabrication of the bracket.

FIG. 5 is a front view of a set of teeth on which brackets have beenmounted holding an arch wire.

FIG. 6 is a side cross-section view of a bracket in accordance with theinvention illustrating the orientation of a metal reinforcement membertherein to provide torque and/or angulation.

FIG. 7(A) is a side view of a bracket in accordance with the inventionwith a reinforcement member therein.

FIG. 7(B) is a side view of the bracket with the reinforcement membermounted therein for providing torque and/or angulation.

FIG. 8 is an enlarged cross-section view of a portion of the basesurface of a bracket in accordance with a second embodiment of theinvention.

FIG. 9 is a photograph illustrating an enlarged top view of the basesurface of the bracket in accordance with another embodiment of theinvention.

FIG. 10 is a photograph illustrating a magnified view of a portion ofthe base surface shown in FIG. 9.

FIGS. 11-14 are front, side, rear and bottom views, respectively, of abracket in accordance with a further embodiment of the invention.

DETAILED DESCRIPTION

A bracket in accordance with a first embodiment of the inventioncomprises a plastic bracket body 1 and a metal reinforcement member 11embedded in the bracket body as shown in FIG. 1. The bracket is a twintype bracket including a U-section slot 2 extending in mesial-distaldirection and two twin-wings 3 at the sides of the bracket to allowligation of an arch wire to the bracket.

The metal reinforcement member 11 is provided to increase the durabilityof the bracket body 1. The reinforcement member 11 includes an elongatedbase 12 and a pair of upward projections or risers 13 on opposite sidesof base 12 giving the reinforcement member a U-shape. A holding notch 14having a width smaller than that of the slot 2 of the bracket body isprovided in the upper center portion of each riser 13. The sides of eachriser 13 form a circular arc 15. When the metal reinforcement member 11is embedded in the bracket body 1, the holding notches 14 of the metalreinforcement member 11 project through the plastic slot surfaces 2 asshown in FIGS. 1-3.

In particular, the holding notches in the metal reinforcement member 11are designed to be spaced about 0.05 to 0.2 mm away from both sides andthe bottom of the slot of the bracket such that the arch wire can beengaged and held substantially only by the holding notches 14 of metalreinforcement member 11.

The metal reinforcement member 11 may be formed by casting, metalinjection molding, stamping or machining and should have a Vickershardness greater than 300. Particularly, if the reinforcement member isstamped, the workpiece should be shaved to remove burrs. Also anysagging on the stamped surfaces should be corrected. The risers 13 ofthe metal reinforcement member 11 forming the holding notch 14 should besufficiently thick to support the arch wire without deformation. Thethickness of the risers in mesial-distal direction is preferably 0.3 to0.5 mm. Although the dimensions of the reinforcement member can bevaried, a total of six varieties including two series of 0.018-inch and0.022-inch thickness, a reinforcement member with a narrow span betweenholding notches for the lower anterior teeth, a wide span for the uppercentral teeth and the upper cuspids, and a medium span for other teeth,should be sufficient to meet commercial requirements.

The bracket body may be transparent comprising a polycarbonate oracrylic resin material or semi-transparent including filler material. Ineither case, the appearance of bracket can be improved by plating orcoating the metal reinforcement member 11 to give it a whiterappearance.

After being stamped, the reinforcement member may be heat treated andtumbled to roughen its outer surfaces. It can then be silver plated.

Adhesion of the reinforcement member to the bracket body was found to besatisfactory when the coating or plating on the reinforcement member was3-7 μm thick and the surface was sufficiently rough. Experimentalresults have found the roughness of the reinforcement surface to be ashigh as 5 to 10 μm after plating, compared with a 1 to 2 μm roughness ofa finished surface of a cold rolled steel plate before plating. Ifincreased adhesive strength is required, a chemical coupling treatmentmay be applied to the plated or coated surface.

The process of forming a bracket 1 with a metal reinforcement member 11embedded therein is illustrated in FIG. 4. A slot forming projection 23is movably located in a fixed mold portion 21 of a mold. The metalreinforcement member 11 is positioned and held on the slot formingprojection as shown in FIG. 4A. The metal reinforcement member 11 can beeither manually or automatically set on the slot projection 23 while themold is in an open position. Next, a movable mold portion 22 of the moldis moved against the fixed mold 21 to close the mold. The base 12 of themetal reinforcement member 11 is held against the projection 23 by apress pin 25 in the movable mold 22 under force of a spring 24. Meltedresin material is then introduced in the mold cavity through a gate 26.The resin material is maintained and cooled in the mold underpredetermined time and pressure conditions, producing a reinforcedplastic bracket like that shown in FIGS. 2 and 3 with a metalreinforcement member 11 therein.

Unlike the prior art, in accordance with the present invention, themetal reinforcement member 11 is not flush with the surfaces of the slot2 of the bracket body. Instead, with the sides of the holding notches 14of the reinforcement member project a distance of about 0.05 to 0.2 mminto the slot 2 of the bracket body 1.

An arch wire can thus be supported in an effective arch wire slot formedby the projected twin holding notches 14 to substantially avoid contactwith the resin slot surface of the bracket body 1. The bracket affixedto a patient's tooth can thus be more easily moved along the arch wire,allowing more effective orthodontic treatment.

Brackets in accordance with the invention are particularly suitable fortooth extraction cases that require significant movement of cuspids orbicuspids. The brackets are particularly suitable in cases whereanterior teeth are crowded as shown in FIG. 5. Because the pair ofholding grooves 14 in each bracket form the arch wire slot of thebracket, the effective distance between brackets on adjacent teeth isincreased. In addition there is a distance of about 0.05 to 0.2 mmbetween each of the two holding notches and the surfaces defining theslot in the bracket body. Accordingly, three-dimensional arch wirecontrol is possible from the initial stages of treatment as a highlyrigid arch wire (W) or an angular arch wire can be bent and used withthe brackets to accelerate orthodontic treatment.

Brackets in accordance with the first embodiment were tested againstprior art plastic brackets. A rectangular arch wire havingcross-sectional dimensions of 0.018-inch by 0.025-inch was connected byligating rings to a bracket in accordance with the invention and to aprior art plastic bracket. The arch wire was then pulled at the speed of0.5 mm/min. The measured load applied by the arch wire on the bracket inaccordance with the invention was 45 to 50 grams. By contrast, the loadon the bracket made of pure plastic was 85 to 90 grams.

The reinforcement member may comprise a precipitation hardenable steelsuch as SUS630 stainless steel. While the reinforcement member 11 inaccordance with the invention preferably comprises a metallic material,other materials like plastics and ceramics may be suitable if thehardness and the coefficient of static friction of these materials issatisfactory.

The metal reinforcement member 11 described above can also be used in abracket providing torque and/or angulation as shown in FIG. 6. Thebracket shown in FIG. 6 can be formed by simply re-orienting the slotforming projection 23 in the mold as needed and inserting thereinforcing member 11 thereon. It is therefore unnecessary to have avariety of metal reinforcement members 11 for use in brackets forparticular teeth, orthodontist techniques or individual patient cases.Brackets in accordance with the invention can therefore be economicallyproduced.

The outer edges of each riser 13 of the metal reinforcement member 11have a circular arc shape 15. Accordingly, the metal reinforcementmember 11 can be oriented in the bracket 1 at various angles, withoutinterference from the edges of the risers 13. A reinforcement member 11of the same design can thus be used in brackets having varying degreesof torque angulation. Mold costs for making reinforcement members canthus be significantly reduced.

A plastic bracket in accordance with a second embodiment of theinvention is similar in structure to the first embodiment describedabove, but is characterized by an improvement to the base surface 4 ofthe bracket 1.

Plastic brackets are normally affixed to a patient's teeth with the useof dental bonding agents like Bis-GMA series composite resin, light curetype Bis-GMA series resin, 4-META adhesive resin and others. Theapplication of a primer on the bonding surface of the bracket isdesirable for obtaining proper adhesion to the teeth. Application of aprimer however increases the number of steps and lengthens the time foraffixing the brackets to the teeth. Therefore, a bracket made of plasticthat can be securely bonded to teeth using a conventional bonding agentwithout use of a primer is desirable.

The bracket in accordance with the second embodiment was formed from aresin or a polycarbonate material filled with a filler material. Thebase surface 4 of the bracket was irradiated with an excimer laser heatray up to a depth of 0.1 to 0.3 mm. The resulting base surface structureprovided an anchoring effect for affixing the bracket to a toothsurface.

In particular, glass beads of 10 to 30 μm diameter were used as thefiller 5. A polycarbonate bracket base filled by volume with 15% glassbeads was irradiated by an excimer laser at an energy density of 1.5J/cm² per pulse at a processing speed of 0.2 μm for about 5 seconds at1000 pulse up to a depth of 0.2 mm. Using a microscope, it was foundthat glass beads were present above the polycarbonate material as shownin FIG. 8 to provide an anchoring structure on the base surface.

The bracket body may also comprise polycarbonate material filled byweight with 30% silica.

Bracket 1 in accordance with the second embodiment were affixed to teethusing a Bis-GMA series composite resin. A shear bond strength of 10 to15 kg was measured for the brackets or 100 to 150 kg/cm² per unit area,which meets the 100 kg/cm² bond strength requirement for usualorthodontic treatment.

While the filler material 5 comprised glass beads in the above example,other inorganic or organic substances can be used. The filler 5 is alsonot limited to solid spherical matter; plate, fibrous, bar materials,hollow spheres, and other matter may also be used.

FIGS. 9 and 10 are enlarged photographs of the base surface 4 of abracket including fibrous filler material therein in accordance with theinvention. FIG. 9 is a view of the entire base surface, and FIG. 10 is amagnified view of a portion of the base surface shown in FIG. 9.

The bracket of FIGS. 9 and 10 comprises polycarbonate plastic with 30%glass fiber filler. The base surface was flashed by an excimer laser toa melting depth of 0.1 mm. Masking was used such that selective portionsof the base surface were flashed. The resulting base surface as shown inFIGS. 9 and 10 includes exposed glass fibrous material that providesanchoring means for securely affixing and mechanically locking the basesurface on a tooth (not shown).

The filler material in the bracket body may be exposed at the basesurface by application of a laser thereon or by other suitable means,including application of a solvent on the base surface.

In a bracket made in accordance with a third embodiment of theinvention, the base surface 4 of the bracket 1 does not include a filler5 as in the previously described second embodiment. Inorganic aluminumoxide powder is applied on the base surface 4 by a plasma injection toform an inorganic phase having a thickness of 0.1 mm. A silane couplingagent is then applied on the inorganic phase.

The bracket 1 in accordance with the third embodiment was measured tohave a shear strength of 15 to 20 kg on the base surface 4, which has anarea of about 10 mm². The adhesive strength of the base surface 4 isabout 150-200 kg/cm² per unit area. The inorganic powder applied byplasma injection was about 10 to 30 μm in diameter. A color of theinorganic phase is white and therefore does not adversely affect theappearance of the bracket.

The brackets previously described were twin type brackets. The presentinvention is however not limited to twin type brackets and is alsoapplicable to single type brackets. A metal reinforcement member used ina single type bracket would include a holding notch as previouslydescribed and be shaped to conform to a single wing design.

In accordance with another embodiment of the invention, the base of abracket including a filler material may be irradiated to form a basesurface that can be securely bonded to a tooth. In accordance with afurther embodiment of the invention, an inorganic phase may be formed onthe base surface of the bracket, and a silane coupling agent may beapplied on the inorganic phase for securely affixing the bracket to atooth. Accordingly, a bracket in accordance with the invention can besecurely bonded to a tooth without need for a wide conventional baseplate that may adversely affect the appearance of the bracket.

A bracket 30 shown in FIGS. 11-14 is marked in accordance with a furtherembodiment of the invention. FIG. 13 is the rear view of the bracket 30illustrating the back of the base 32 of the bracket 30, that is, thelingual surface 34 of the bracket, which is adapted to be affixed to atooth (not shown). Identification characters 35 (shown for example as"U3L" in the drawing) are molded in recessed portions 36 of the lingualsurface 34 of the bracket 30. An important advantage of locating theidentification characters 35 on the lingual surface 34 is that aftercement or other bonding material is applied to the lingual surface 34 tobond the bracket 30 to the tooth, the reference characters should not benoticeable. If the reference characters are molded on the oppositelabial surface 37 of the bracket 30, the projections or indentationsdefining the marking may reflect light and adversely affect theaesthetic appearance of the bracket 30.

FIG. 11 illustrates a suitable marking of the labial surface 37 of thebracket 30, which acts as a positioning guide allowing the practitionerto properly align the bracket on a tooth during installment without useof a height gauge. In the drawing, a pair of crossed lines 39 are shownas an example of such a marking. The marking is made with an ink that isnon-toxic and soluble such that when placed in an oral environment, itquickly dissolves and is removed from the labial surface or it can beeasily brushed off with a tooth brush during usual brushing. The markingwill thus not affect the appearance of the bracket when in use.

The lines 39 of the marking each comprise a plurality of dots that canbe ink jet printed on the bracket. A very small amount of ink is neededfor the marking (about 8.3×10⁻⁷ cc per dot). The ink is soluble inwater, alcohol or MEK. The ink may have one of several colors, includingfor example, black, yellow, red and blue.

In summary, a bracket in accordance with the invention allows an archwire to be held in an effective arch wire slot formed by a holding notchof a reinforcement member embedded in the bracket body. Accordingly, thearch wire substantially avoids contact the resin slot surface. Thereinforcement member thus increases the durability of the plasticbracket while allowing the bracket to be smoothly moved along an archwire when secured to a tooth.

A reinforcement member of the same design can be used in brackets withor without torque and/or angulation. It is therefore unnecessary to havea variety of reinforcement members for use in different brackets to meetthe needs of different types of teeth, orthodontist techniques, andindividual patient cases as previously required.

Further, the bracket of this invention may be enhanced with fillermaterials on the base for enhancing bonding to the tooth. Also, thebracket may be provided with identification and alignment characters andmarkings that facilitate its use by the practitioner.

We claim:
 1. An orthodontic bracket for attachment to a patient's tooth,said bracket including a labial surface and a lingual surface, andcomprising a removable character marking on said labial surface.
 2. Anorthodontic bracket for attachment to a patient's tooth, said bracketincluding a labial surface and a lingual surface, and comprising aremovable marking on said labial surface, wherein said marking comprisesa pair of crossed lines, each comprising a plurality of dots.
 3. Anorthodontic bracket for attachment to a patient's tooth, said bracketincluding a labial surface and a lingual surface, and comprising aremovable marking on said labial surface, further comprising a markingon said lingual surface, wherein said marking on said lingual surfacecomprises molded identification characters.
 4. An orthodontic bracketfor attachment to a patient's tooth, said bracket including a labialsurface and a lingual surface, and comprising a character marking onsaid lingual surface.
 5. The orthodontic bracket of claim 4, furthercomprising a removable marking on said labial surface.
 6. Theorthodontic bracket of claim 5, wherein said marking on said labialsurface comprises a soluble, non-toxic marking adapted to be removablein an oral environment.
 7. An orthodontic bracket for attachment to apatient's tooth, said bracket including a labial surface and a lingualsurface, and comprising a marking on said lingual surface, wherein saidmarking comprises molded identification characters.
 8. An orthodonticbracket for attachment to a patient's tooth, said bracket including alabial surface and a lingual surface, and comprising a marking on saidlingual surface, wherein said lingual surface includes at least onerecessed portion and wherein said marking comprises a moldedidentification character position in said recessed at least one portion.